:( started my mower engine without oil!! I think my engine burned. Is it thrashed? Or can it be fixed?

It depends how long you ran it. Did it freeze up?
Add oil in crankcase first.

Take out plugs. Squirt light weight oil in cylinders and hand crank it over slowly.

If it feels free use electric start or pull handle.

After that get pistons to its highest point in the cylinder and use a clean soft rag and a screwdriver handle to wipe out excess oil.

Put plugs back in and see if it runs and how bad it may smoke or noise in the crank case.

If it does seem to run all right then change oil and filter after warm up. It may run for awhile if at all.

To answer the question the engine would need torn down and inspected

It depends how long you ran it. Did it freeze up?
Add oil in crankcase first.

Take out plugs. Squirt light weight oil in cylinders and hand crank it over slowly.

If it feels free use electric start or pull handle.

After that get pistons to its highest point in the cylinder and use a clean soft rag and a screwdriver handle to wipe out excess oil.

Put plugs back in and see if it runs and how bad it may smoke or noise in the crank case.

If it does seem to run all right then change oil and filter after warm up. It may run for awhile if at all.

To answer the question the engine would need torn down and inspected

:)I talked to a friend of mine that does small engine repairs and he said we will do what you suggested. Thanks :)